JPH0983289A - Surface acoustic wave device, and receiver and communication system using the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an output of a matched filter at a high level efficiently by arranging one input comb-like electrode and two output comb-like electrodes onto a piezoelectric substrate so as to propagate surface acoustic waves in both directions generated from the input IDT effectively. SOLUTION: An input IDT 121 formed on a piezoelectric substrate 102 stimulates an input code string signal being a SAW signal. Electrode finger pairs of output IDTs 131 arranged in matching with a prescribed code string receive the SAW signal. Then the surface acoustic wave device is used for a matched filter by detecting the code string signal coincident with the code string. The SAW signal generated from the input IDT 121 is given at first to the electrode finger pair at the end of receiving the SAW signal in the 1st output IDT 131. Then after a time equivalent to one-chip length of the code string, the code string is fed at first to the electrode finger pair at the end of the input of the 2nd output IDT 132. The signal is sequentially given to the electrode finger pair closer to the input of the 1st output IDT and the 2nd output IDT alternately after the time equivalent to one-chip length of the code string.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device used in a SAW matched filter using a surface acoustic wave using a piezoelectric element, a spread spectrum receiving device using the same, and a communication system.

[0002]

2. Description of the Related Art In recent years, surface acoustic waves (SAW: Surface Ac)
oustic Wave) is electromechanical functional elements using a filter, resonator, although actively addressed in various fields such as delay lines, it is the number of 1/10 ^-5 in comparison with the sound velocity waves of the elastic waves km / Since it is possible to miniaturize the equipment, the energy of the wave is concentrated near the surface of the propagation medium, and the expectation that the generation, detection, and control of surface acoustic waves can be processed on the solid surface, and IC manufacturing. This is because the technology can be applied.

As an example of application to the signal processing of surface acoustic waves having such characteristics, there is a spread spectrum (SS) communication system, which has a frequency band much wider than the original bandwidth of the signal to be transmitted. It is transmitted after being spread / converted to a coded signal sequence that it has, and it is detected by a receiving device that responds only to that coded signal sequence or obtains a high correlation peak in that coded signal sequence The matching filter of this surface acoustic wave element is used as an element that responds only to the encoded signal sequence when reproducing the signal.

In recent years, the SAW matched filter, particularly the matched filter using surface acoustic waves, has been important as a device for establishing synchronization for performing synchronization acquisition / synchronization tracking in performing spectrum spread (SS) communication. Sex is increasing.

FIG. 10 is a conceptual diagram showing a SAW matched filter using such a conventional surface acoustic wave element.
In the figure, 101 is a stem for fixing a matched filter chip, 102 is a piezoelectric substrate such as ST cut crystal fixed on the stem 101, 111 is an input comb-shaped electrode (IDT; InterDig) for converting an input electric signal into a surface acoustic wave signal.
Ital Transducer), 121 is a pin for supplying an input IF signal in which the spectrum-spread signal is adjusted to the input center frequency of the matched filter, and 122 is a pin for extracting an output signal. Reference numeral 131 denotes an output IDT, one electrode of which takes an output from the pin 122, and the other electrode of which is connected to the stem 101 serving as a ground potential,
311, 1312, 1313, ... 131X are output I
It is a pair of DT electrode fingers. This electrode finger pair 1311, 131
The electrode direction of 2, 1313, ... 131x, that is,
Which electrode the electrode finger connected to is placed on the input IDT side depends on the pseudo noise (P
N: Pseudo Noise) Determined according to the code string of the code signal.

For example, in the case of FIG. 10, assuming that the output electrode finger pair is a code string of 1101 ... 01 (the last 1 is the earliest code of the input code string), the input code string. Is 1101 ...... 01 (the last 1 indicates the first code).
When input every time, the correlations match and a large correlation peak can be obtained. In addition, the distance between these electrode finger pairs is set to P when the SAW signal generated from the input IDT 111 is
It corresponds to the propagation distance of one chip length of the N code string.

These electrodes are made of a conductive material such as aluminum, and are formed by mounting a metal material such as vapor deposition or coating on the piezoelectric substrate and using the photolithography technique or the like as in the IC manufacturing technique.

In the surface acoustic wave device having such a configuration, when an electric signal having a carrier angular frequency ω obtained by multiplying the input IDT 111 by a PN diffusion code is input, the electric signal is converted into a SAW signal by the piezoelectric effect of the substrate. For example, when the PN spread code is a binary signal, a SAW signal whose phase is inverted each time the code value changes is output from the input IDT 111 and propagates to both sides. In the output IDT 131, I
Electrode finger pairs 1311, 1312, 13 forming a DT
The electrode directions of 13, ..., 131x are determined according to the code used for the PN code string, and the distance between these electrode finger pairs is the SAW generated from the input IDT 111.
Since the signal corresponds to the propagation distance of the one-chip length of the PN code string, only when the SAW signal output from the input IDT 111 propagates for the entire code length, the input IDT 111 transfers to the output IDT 131. The propagated SAW signal and output electrode finger pairs 1311, 1312, 131
.., 131x all have the same phase, and a large output electric signal is obtained. Since this signal is output every time one PN code string has been transmitted through the output IDT 131, a code synchronization signal is obtained. The mechanism of such a SAW matched filter is "surface acoustic wave engineering;
The Institute of Electronics, Information and Communication Engineers, Supervised by Mikio Shibayama ”.

[0009]

However, in the case of such a SAW matched filter, the input IDT 111
SAW is excited in both directions, and the output IDT1
At 31 as well, half the energy of the signal is lost due to the bidirectionality of the re-excited SAW, resulting in a loss of 6 dB for both. In order to avoid this loss, a method of making the input / output IDT a unidirectional IDT is conceivable. However, like the matched filter, the logarithm of the input / output IDT (in the case of the output IDT, the logarithm of the electrode finger pair per code) is used. In a SAW filter that cannot be increased, the unidirectional IDT that uses the SAW reflection condition does not have sufficient unidirectionality, and in the case of the three-phase unidirectional IDT, the impedance of the input IDT is high. There is a problem in that it is difficult to manufacture the phase shifter, and even if the phase shifter can be manufactured, the loss in the phase shifter is large.

[0010]

The present invention has been made to solve the above problems, and an input code string signal is formed by an input comb-shaped electrode (hereinafter referred to as an input IDT) formed on a piezoelectric substrate. Is received as a surface acoustic wave (hereinafter referred to as SAW) signal, and the SAW signal is received by the electrode finger pair of an output comb-shaped electrode (hereinafter referred to as output IDT) arranged in accordance with a predetermined code string. A surface acoustic wave device used for a SAW matched filter that detects a signal of a code string that matches the above-mentioned code string, having at least two output IDTs, and the two output IDs.
T and the input IDT are first input to the electrode finger pair at the end of the side (hereinafter, referred to as the input side) where the SAW of the first output IDT is input from the SAW signal generated from the input IDT at a certain time. After the time of one chip length of the code string is input, it is input to the electrode finger pair at the end on the input side of the second output IDT, and then the first output IDT is alternated every time of one chip length of the code string. , The second output IDTs are arranged so as to be sequentially input from the electrode finger pair closer to the input side.

Further, according to the present invention, an input code string signal is excited as a surface acoustic wave (hereinafter referred to as SAW) signal by an input comb-shaped electrode (hereinafter referred to as input IDT) formed on a piezoelectric substrate, A SAW matched filter that detects a signal of a code string that matches the code string by receiving the SAW signal with an electrode finger pair of an output comb-shaped electrode (hereinafter, referred to as an output IDT) that is arranged according to a predetermined code string. A surface acoustic wave device for use in, having at least two output IDTs,
T and the input IDT are first applied to a pair of electrode fingers at the end (hereinafter, referred to as the input side) where the SAW signal generated from the input IDT at a certain time is input to the SAW of the second output IDT. After that, the input sequence is sequentially input from the electrode finger pair closer to the input side of the second output IDT every time of one chip length of the code string, and finally input from the electrode finger pair of the second output IDT. After the time of the code string 1 chip length after being input to the input electrode finger pair, the code string is input to the electrode finger pair at the input side end of the first output IDT, and then the code string 1 chip length One of the output IDTs is arranged so that the electrode finger pairs closer to the input side of the input IDT are sequentially input.

In this way, since the surface acoustic waves in both directions generated from the input IDT can be effectively transmitted, a high level matched filter output can be obtained efficiently.
Further, only the output IDT having a small impedance is a three-phase unidirectional IDT. As a result, both SAW energies excited in both directions at the input IDT can be used, and thus the loss at the input IDT can be improved by 3 dB. Moreover, since the output IDT has a low impedance, a phase shifter can be easily manufactured, and there is almost no loss in the phase shifter. Therefore, by making the output IDT a unidirectional IDT, the loss can be further improved by 3 dB. By using such a surface acoustic wave device for a receiving device and a communication system of a spread spectrum communication system, the transmitted spread signal can be effectively secured.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings together with each embodiment.

(Embodiment 1) FIG. 1 is a schematic view of a surface acoustic wave (SAW) matched filter of the present invention. In the figure, 101 is a stem for fixing a matched filter chip, 102 is a piezoelectric substrate such as lithium niobate and ST cut quartz, 111 is an input IDT for converting an electric signal into a surface acoustic wave signal, and 121 is a spread spectrum code. I in which the column signal is adjusted to the input center frequency of the matched filter
An input pin for supplying an F signal and an output pin 122 for extracting an output signal are connected to the counter electrode of the input electrode 111 and the counter electrode of the output electrode 131 to the ground level stem. Also, 131 and 132 are output IDs, respectively.
T, 1311, 1312, 1313, ..., 1
31x is a pair of electrode fingers of the output IDT 131, 1321, 13
, 132x are output IDTs 132.
Electrode pair of. These electrode finger pairs correspond to the input IDT1
The SAW signal generated from 11 is arranged at an interval corresponding to twice the distance propagated in the time of one chip length of the code string,
The electrode finger pair of the two output IDTs 131 and 132 is the input ID
The SAW generated from T111 is arranged so as to be displaced from the input IDT by a distance corresponding to the distance propagated in the time of one chip length of the code string. That is, the input IDT11
1 and the output IDTs 131 and 132 are electrode finger pairs 1 at the end (input side) where the SAW signal generated from the input IDT 111 at a certain time is input to the SAW signal of the output IDT 131.
It is arranged so that it is first input to 311 and is sequentially input from the electrode finger pairs closer to the input side of the output IDTs 131 and 132 alternately at intervals of one chip length of the code string. The interval between each electrode finger is λ / 2, and the line width of each electrode finger is λ / 4.

That is, in FIG. 1, after the SAW signal generated from the input IDT is detected by the electrode finger pair 1311, the electrode finger pair 1321, 1312, 1322, 1322, 1321, 1322 is generated at every time corresponding to one chip length of the code string. 1313, ... The electrode finger pairs 1311, 1321, 131
2, 1322, 1313, ..., 131x, 132x
Of the electrode, that is, which electrode finger is connected to the input IDT side is determined according to the PN code of the signal input to the input IDT. Electrode finger pairs 1311, 1321, 1312, 1322, 13
The signals detected by 13, ..., 131x, 132x are added in the electrodes, and the PN signal input from the input IDT propagates as a SAW signal, and is large only when the electrode directions of all the electrode finger pairs match. The signal is obtained.

This point will be described more specifically with reference to the structure of each output electrode finger pair in FIG.
1, 1312, 1322, 1313, ..., 131
x and 132x are 11010011 ... 0011, for example.
(The last 1 is the earliest code in the input code string.)
If the code string excited by the input IDT is 11010011 ... 0011 (the last 1 indicates the earliest code), a signal level with a high correlation peak can be obtained. Therefore, in the communication system, if the transmitting side and the receiving side output / input in the above relationship, demodulation can be performed on the receiving side so that the code strings match, and the baseband signal on the transmitting side can be reliably and reliably received on the receiving side. It can be demodulated highly. In this case, with respect to the input IDT, the output IDTs in both directions are electrode finger pairs having a structure that alternately matches the input code string, and at a distance of half the output IDT with respect to the output IDT in one direction. It will be good.

Further, the piezoelectric substrate used for the SAW matched filter may be a piezoelectric body itself or a non-piezoelectric body provided with a piezoelectric body film, as long as it has piezoelectricity. Also, the piezoelectric substrate is stable against environmental changes if the SAW propagation velocity change due to temperature is approximately 0 or if the SAW propagation velocity change due to temperature is approximately 0 by attaching a thin film on the piezoelectric substrate. Since the correlation peak can be obtained, it is possible to suppress the characteristic change due to temperature by using a YZ cut surface of lithium niobate as the material of the piezoelectric substrate.

In the case of the above-mentioned configuration, since the SAW that advances in both directions of the input IDT is used, a signal of a level twice that of the conventional SAW matched filter is obtained,
[Output correlation peak level / input signal level] efficiency is 3
Improves dB. Further, the SAW signal propagating from the input IDT is partially converted into an electric signal every time when passing through the electrode finger pair of the output IDT, so that the SAW signal becomes gradually smaller and the electrode of the output IDT separated from the input IDT. Although the energy converted into an electric signal becomes small in the finger pair, according to the present invention, the electrode finger pair of each output IDT becomes half of that in the conventional case, so that each electrode finger pair distant from the input IDT reaches. The SAW signal is increased, and as a result, the above efficiency is further improved.

The entire SAW matched filter is increased by the distance between the output IDT and the input IDT in one of the two directions. However, as described above, at least 3 dB or more improvement in efficiency is obtained when the communication system is used. SAW
It is very useful for signal processing in the decoder after the matched filter.

(Embodiment 2) FIG. 2 is a block diagram showing another embodiment of the present invention. In the figure, the same symbols as those in FIG. 1 have the same functions and shapes, and detailed description thereof will be omitted. In FIG. 2, the output IDT 131 is an IDT for detecting the first half code of the PN signal, and the output IDT 132 is an IDT for detecting the second half code of the PN signal. 1311,
1312, 1313, ..., 131x, and 132
Output I of 1, 1322, 1323, ..., 132x
The electrode finger pair of DT is arranged at an interval corresponding to the distance that the SAW signal excited and generated from the input IDT 111 propagates in the time of one chip length of the code string, and the electrode finger pair 1311 and 1
32x is arranged such that the SAW generated from the input IDT 111 is displaced from the input IDT 111 by a distance corresponding to the distance that the SAW propagates in the time of one chip length of the code string.

That is, the input IDT 111 and the output IDT
In 131 and 132, the SAW signal generated at a certain time from the input IDT 111 is first input to the electrode finger pair 1321 at the end (input side) of the output IDT 132 to which the SAW signal is input, and the one chip length of the code string is set. Output IDT after time
It is input to the second electrode finger pair 1322 from the input side of 132, and then output IDT 13 at every time of one chip length of the code string.
The electrode finger pair 132X that is input last among the two electrode finger pairs
Is input to the electrode finger pair 1311 at the input side end of the output IDT 131 after a time of one chip length of the code string, and thereafter the output IDT is output for each time of one chip length of the code string.
The electrode finger pairs closer to the input side of the electrode 131 are arranged so as to be sequentially input. In this embodiment, the output IDT 131
At the same time that the correlation peak in the first half of the code is output
Although the correlation peak in the latter half of the code is output at T132, it is not necessary to use a circuit or the like for delaying at least one of the signals input to the two output IDTs due to the above arrangement.

With this configuration, after the beginning of the code of the signal excited and output from the input IDT reaches the output IDT 131, the latter half of the code of the signal output from the input IDT reaches the output IDT, and the first half of the code is At the same time that the output IDT 131 overlaps and outputs the correlation peak, the latter half of the code overlaps on the output IDT 132 and outputs the correlation peak. Eventually, the electrode finger pairs of all the output IDTs 131 and 132 match the input code string. Then, the added output of each electrode finger pair has a peak.

In the case of the above arrangement, the output IDT 132 has the electrode finger pair only in the vicinity of the input IDT 111, so that it can be made smaller than in the first embodiment.

Also in the case of this embodiment, the correlation peak can be obtained when the one-chip length of the input code string reaches.
If the chip length is not reached or if it exceeds 1 chip length, the next 1
Since the correlation is deviated during the period up to the chip length, a high level of the correlation peak cannot be obtained. In this way, the correlation peak corresponding to the strong correlation can be obtained.

(Embodiment 3) FIG. 3 is a schematic view when the electrode fingers of the input IDT and the output IDT of the surface acoustic wave (SAW) matched filter of Embodiment 1 or Embodiment 2 of the present invention are split electrodes. is there. For matched filters,
Time until SAW passing through the electrode finger pair of the output electrode reaches the next electrode finger pair, and SAW reflected by the same electrode finger pair
Since it takes the same time to reach the previous electrode finger pair or the input IDT, it is necessary to eliminate the influence of the reflected wave that becomes a noise source. FIG. 3B is an enlarged view of the electrode finger pair of the output IDT shown in FIG. The split electrode shown in FIG. 3 (B) is
As a means for suppressing the reflected wave in the SAW device,
By setting the line width of the electrode fingers to be λ / 8 and the spacing between the electrode fingers to be λ / 8, the SAW excited by the input IDT travels only in both directions, and each unidirectional shape SAW can be obtained. Therefore, as the SAW progresses in both directions, each output I
A signal level of a high S / N correlation peak with a small noise component can be obtained from each electrode finger pair of the DT 131 and 132, and also in the SAW matched filter according to the present invention,
Using this embodiment is an effective means.

(Embodiment 4) FIG. 4 shows the output ID of the surface acoustic wave (SAW) matched filter of the present invention shown in Embodiment 1.
FIG. 7 is a schematic view of an example in which T is replaced with a three-phase type unidirectional IDT. In the figure, the same reference numerals are used for the same functions as those in FIG. 1, and detailed description thereof will be omitted. here,
The input IDT 111 is SA that advances to both ends of the electrode finger pair.
Excite W. A 60 ° phase shifter 200 is inserted between the pins 122 and 123 connected to the two output electrodes having different phases, and the other electrode is held at the ground potential. By connecting and configuring in this way, assuming that the phase difference between the output electrode finger connected to the pin 122 and the electrode finger connected to the ground electrode is 0 °, the output connected to the pin 122 is output. The phase difference between the electrode finger and the output electrode finger connected to the pin 123 is (180-60 =) 12
It becomes 0 ° and functions as a three-phase type unidirectional IDT.

Normally, the output IDT of the matched filter is P
Since each N code has one to two pairs of electrode fingers, the output IDT in a system having a long PN code
The number of electrode finger pairs is increased, and the impedance of the output IDT is lowered. Here, if the impedance of the three electrodes of the output IDT is Z, the impedance Z of the 60 ° phase shifter is
o is Zo = Z (1−EXP (jπ / 6)), and the impedance of the phase shifter can be reduced in proportion to the impedance Z of the electrode. Generally, the impedance of the IDT is capacitive, and the phase shifter 200 is required to have an inductive impedance. Therefore, if the impedance of the phase shifter 200 is small, the phase shifter 200 can be configured with a small coil, so that the loss is small. The phase shifter 200 can be configured.

Thus, the three-phase type unidirectional IDT according to the present embodiment is constructed, and each electrode finger pair of the output IDT has an electrode finger pair 1311, 1321, 1312, 1322, 13
13, 1323, ... Output pins 122 and 12 obtained with a phase difference of 120 ° when the code strings corresponding to 131X and 132X match the code strings excited from the input IDT.
A correlation peak can be obtained from the signal of No. 3, and if this signal is converted into a two-phase signal through a three-phase / two-phase converter, the merit of unidirectionality, the output impedance can be lowered, and the three-phase electrode finger pair With, it is possible to obtain a high correlation peak and obtain a large ratio between the case where there is no correlation and the correlation peak, and the like, and a signal with a large S / N can be obtained.

(Embodiment 5) FIG. 5 is a schematic view of an embodiment in which a means for concentrating SAW is inserted between an input IDT and an output IDT in the present invention. In the SAW matched filter, since the number of pairs of electrode fingers of the output IDT per code is as small as 1 to 2, the frequency band is determined by the number of pairs of electrode fingers of the input IDT 111. When a matched filter is used for spread spectrum communication, even a synchronization-dedicated code is a spreading code and requires a wide frequency band, so the upper limit of the logarithm of the input IDT is determined by the frequency bandwidth. On the other hand, the impedance of the IDT is determined by the logarithm of the IDT and the cross width, so that if the logarithm is reduced, the input impedance increases and it becomes difficult to achieve impedance matching. On the other hand, since the output IDT has a large number of pairs of electrode fingers, the impedance becomes small and it becomes difficult to achieve impedance matching.

The present embodiment is a means for solving this,
A means for converging the SAW is provided between the input IDT and the output IDT by widening the crossing width of the input IDT and narrowing the crossing width of the output IDT. In FIG. 5, an example using a horn as a means for concentrating SAW is shown. This is because the metal vapor deposition part that forms the horn is more SAW than the non-metal deposition part.
Is slowed down, and the total reflection condition is satisfied depending on the propagation direction of the SAW reaching the horn. Utilizing this condition, the trapezoidal inclined portion is used as the front reflecting surface to concentrate the SAW on the output IDT side in both directions. In this way, since the input and output impedances are matched and the electrode finger pairs of both output IDTs are concentrated, a high correlation peak can be obtained. FIG.
Also in this embodiment, the code strings of the signals excited from the input IDTs are correlated by matching the code strings of the electrode finger pairs of the left and right output IDTs with the code strings alternately arranged on the right, left, and left in the figure. The peak can be obtained.

In the case of this SAW matched filter, since the collected SAWs must be propagated for a long distance, an acoustic lens having a structure like an optical beam compression lens may be used instead of the horn type.

(Embodiment 6) When the SAW is propagated for several tens of wavelengths or more, since the SAW propagates as a plane wave having an opening at the intersection width of the input IDTs, diffraction occurs at the end portions where the electrode fingers intersect. , SAW spreads. In order to suppress the spread of the SAW due to diffraction, the SAW excitation may be reduced toward the end of the intersection of the IDTs and increased in the central portion. Based on this idea, it is an abodized electrode that the crossing width of each electrode finger is changed so that many electrode fingers cross at the central portion and the electrode index at which the electrode fingers cross at the ends is reduced. FIG. 6 is a schematic view of an embodiment in which the input IDT is an abodized electrode in the present invention. By adopting an addoise electrode for the input IDT of the matched filter of the present invention, a highly efficient matched filter can be constructed.

Therefore, by using an abodized electrode in which the number of crossing electrode fingers is increased and the crossing width on the outer side is made smaller than that of the structure of the input IDT according to the above-mentioned embodiment, a large S value can be accurately obtained.
By preventing the spread SAW by allowing the AW to be excited and making the transmission region only in the direction of both output IDTs, the electric signal appearing at each electrode finger pair of both output IDTs can be made high, and the correlation peak at the time of correlation is at a high output level. Can be obtained at

In the above embodiment, the example of two output IDTs with respect to one input IDT is shown, but at least two output IDTs are sufficient, and one surface has a predetermined interval in three or more directions. An output IDT having a sign may be arranged.

(Embodiment 7) FIG. 7 is a block diagram showing an example of a communication system using a SAW matched filter composed of output IDTs at both ends for receiving SAWs propagating in both directions of an input IDT as described above. Is. In the figure, 40 in the upper stage indicates a transmitter. This transmitting apparatus spread-spectrum modulates a signal to be transmitted using a spread code and transmits it from an antenna 401. The transmitted signal is received by the receiving device 41 and demodulated. The receiving device 41 includes an antenna 411, a high frequency signal processing unit 412,
Synchronization circuit 413, code generator 414, spread demodulation circuit 41
5, demodulation circuit 416.

The received signal received by the antenna 411 is appropriately filtered and amplified by the high frequency signal processing unit 412, and is output as it is as the transmission frequency band signal or as an appropriate intermediate frequency band (IF) signal. The signal is input to the synchronizing circuit 413.

The synchronizing circuit 413 processes the signals output from the SAW matched filter 4131 of the surface acoustic wave device using the surface acoustic wave (SAW) element described in the above embodiment of the present invention and the surface acoustic wave device 4131. , A code generator 4 for generating a spread code synchronization signal and a clock synchronization signal for the transmission signal.
It is composed of a signal processing circuit 4133 which outputs the signal to the fourteen. SAW
The output signal from the high frequency signal processing unit 412 is input to the surface acoustic wave device 4131 which is a matched filter, and the synchronization-specific spreading code component included in the reception signal and the code array of each electrode finger pair of the output IDT of the SAW matched filter 4131. The correlation peak is output when the polarities of and match. Therefore, the SAW matched filter described in each of the above embodiments does not interfere with noise, has a high correlation peak, and S
It is possible to obtain a synchronization signal with good / N.

The signal processing circuit 4133 detects the correlation peak from the synchronization signal input from the SAW matched filter 4131, reproduces the clock signal, and outputs the spread code synchronization signal and the clock signal to the code generator 414. After synchronization is established, the code generator 414 generates a spread code whose clock and spread code phase match the spread code on the transmission side. This spread code is output to the spread demodulation circuit 415, and the spread demodulation circuit 415 restores the signal before spread modulation. The signal output from the spread modulation / demodulation circuit 415 is a signal modulated by a generally used modulation method such as so-called frequency modulation or phase modulation, and data demodulation is performed by the demodulation circuit 416 corresponding to the modulation circuit. It

Since a high correlation peak can be obtained by using the SAW matched filter of the two-sided output IDT corresponding to the input IDT in this embodiment, the synchronization signal synchronized with the wide band spread signal can be synchronously captured at high speed. Since synchronization can be followed, highly reliable and stable communication is possible, and it can contribute to a small and portable structure.

Regarding the synchronization acquisition, as an example, SAW
There is an example of using a convolver. In this case, a spread code is output from the SAW convolver through a signal processing circuit and input to a code generator, and the output of this code generator is output to this SAW.
Although it was necessary to negatively feed back to the convolver to synchronize with the input signal, in the SAW matched filter shown in this embodiment, the SAW matched filter itself has the electrode finger pair of the output IDT that matches the input code string. Since the SAW matched filter can directly output a high correlation peak when a predetermined code string is input from the input without using a negative feedback loop, the circuit configuration is simplified. In addition, a high-speed response can be achieved. In particular, the added output from each electrode finger pair of the output IDTs arranged on both sides of the input IDT is extremely efficient, and a high S / N correlation peak can be obtained.

(Embodiment 8) FIGS. 8 and 9 are block diagrams showing an example of a transmitter and a receiver of a CDM communication system using the surface acoustic wave element as described above. In FIG. 8, 501 is a serial-parallel converter that converts serially input data into n parallel data, and 502-1 to n are n parallel data and n output from the spread code generator 503. , 503 denotes n different spreading codes PN1, PN2, ... P.
A spread code generator for generating Nn and a spread code PN0 dedicated to synchronization, and 504 is an adder for adding the synchronization dedicated spread code output from the spread code generator 503 and n outputs of the multiplier groups 502-1 to 502-n. , 505 are high frequency stages for converting the output of the adder 504 into a transmission frequency signal, and 506 is a transmission antenna.

In FIG. 9, 601 is a receiving antenna, 602 is a high frequency signal processing section, and 603 is the SAW matched filter described in the above embodiment for capturing, tracking and maintaining the synchronization with the spreading code and clock on the transmitting side. The reference numeral 604 denotes the same synchronization circuit, and 604 uses the code synchronization signal and the clock signal input from the synchronization circuit 603 to provide the same n + 1 spreading codes PN and the reference spreading code PN as the spreading code group on the transmission side.
A spreading code generator for generating 0, 605 for a carrier reproducing spread code PN0 output from the spreading code generator 604 and a carrier reproducing circuit for reproducing a carrier signal from the output of the high frequency signal processing unit 602, and 606 a carrier reproducing circuit 605.
, The output of the high-frequency signal processing unit 602, and the output of the spreading code generator 604, the baseband demodulation circuit for demodulating in the baseband using the n spreading codes PN, and 607 is the output of the baseband demodulation circuit 606. It is a parallel-serial converter that performs parallel-serial conversion on certain n pieces of parallel demodulated data.

In the above-mentioned structure, at the transmission side, the input data is first converted by the serial-parallel converter 501 into n pieces of parallel data equal to the number of code division multiplexes. On the other hand, the spread code generator 503 generates spread codes PN0 to PNn having n + 1 code periods that are the same but different from each other. Of these, the spread code PN0 is dedicated to synchronization and carrier reproduction, and is not modulated by the parallel data and directly added by the adder 50.
4 is input. The remaining n spread codes PN1 to PN are multiplied by n parallel data in the multiplier groups 502-1 to 50n.
It is modulated and input to the adder 504. Multiplier group 502
The n pieces of parallel data obtained in -1 to n are spread signals each having a broadband frequency spectrum. The parallel data adder 504 linearly adds the input n + 1 signals and outputs the added baseband signal to the high frequency stage 505. Subsequently, the baseband signal is converted into a high-frequency signal having an appropriate center frequency in the high-frequency stage 505 and transmitted from the transmission antenna 506.

On the receiving side, the signal received by the receiving antenna 601 is appropriately filtered and amplified by the high frequency signal processing unit 602, and is output as it is as a transmission frequency band signal or an appropriate intermediate frequency band (IF) signal. To be done. The signal is input to the synchronization circuit 603. Synchronous circuit 6
Reference numeral 03 is a SAW matched filter which is the SAW matched filter described in the above embodiment of the present invention, and a signal output from the surface acoustic wave device 6031 is processed to spread the spread code synchronization signal and the clock synchronization signal with respect to the transmission signal. A signal processing circuit 6033 for outputting to the code generator 604.

An output signal from the high frequency signal processing unit 602 is input to the surface acoustic wave device 6031 which is a SAW matched filter. Here, in the surface acoustic wave device 6031,
The synchronization-only spread code component included in the received signal and the array polarity of the electrode fingers matching the code of the output electrode finger pair of the surface acoustic wave device 6031 match on the output electrode finger pair array of the surface acoustic wave device 6031. Sometimes a high correlation peak is output, which makes it possible to obtain a high S / N synchronization signal. If they do not match, the output level of the electrode finger pair array is low, and a synchronization signal cannot be obtained. In the signal processing circuit 6033, the correlation peak is detected from the signal input from the surface acoustic wave device 6031, the transmitted clock signal of the spread code PN0 is regenerated, and the code synchronization signal and the clock signal are output to the spread code generator 604. To be done.

After the synchronization is established, the spreading code generator 604 generates a spreading code group in which the clock and the spreading code phase match the spreading code group on the transmitting side. The spreading code PN0 dedicated to synchronization of these code groups is input to the carrier reproducing circuit 605. The carrier reproduction circuit 605 despreads the received signal converted to the transmission frequency band or the intermediate frequency band, which is the output of the high frequency signal processing unit 602, with the synchronization-dedicated spreading code PN0, and reproduces the carrier wave in the transmission frequency band or the intermediate frequency band. To do. As the configuration of the carrier reproducing circuit 605, for example, a circuit using a phase locked loop is used. The received signal and the spread code PN0 for synchronization are multiplied by the multiplier. After the synchronization is established, the clock and code phase of the synchronization-specific spreading code in the received signal and the reference synchronization-specific spreading code are the same, and the synchronization-specific spreading code PN0 on the transmitting side is not modulated with data. Is despread at, and a carrier component appears at the output. The output is then input to a bandpass filter, and only the carrier component is extracted and output. The output is then input to a well-known phase-locked loop consisting of a phase detector, a loop filter, and a voltage-controlled oscillator, which locks the phase to the carrier component output from the band-pass filter from the voltage-controlled oscillator. The signal is output as a reproduced carrier.

The reproduced carrier wave is input to the baseband demodulation circuit 606. The baseband demodulation circuit 606 generates a baseband signal from the reproduced carrier wave from the carrier reproduction circuit 605 and the output of the high frequency signal processing unit 602. The baseband signal is divided into n pieces and is despread for each code division channel by the spread code groups PN1 to PNn which are the outputs of the spread code generator 604, and then data demodulation is performed as a parallel signal. The parallel demodulated n demodulated data are converted into serial data by the parallel-serial converter 607 and output.

Although the present embodiment is a case of binary modulation, other modulation methods such as quadrature modulation may be used. Further, by using the SAW matched filter in the communication system,
Compared with the conventional case where a feedback loop such as a PLL circuit is configured for synchronization tracking, a lead-in time for feedback is unnecessary, and not only the circuit-like operation but also a simple configuration can be achieved, thus reducing the size. It is extremely effective for mobile communication systems that require

In particular, the SAW is excited on both sides of the input IDT, and the electrode finger pairs of the output IDTs arranged on both sides are used to
Also, as a unidirectional or three-phase unidirectional, horn type, SAW matched filter such as an avoded electrode, etc., a high level correlation peak can be obtained and a high S / N is obtained, so jitter due to noise is suppressed. Therefore, the stability of synchronization of the synchronization acquisition and the subsequent synchronization tracking is increased, and the reliability of the communication system can be improved.

[0050]

As described above, according to the present invention, a highly efficient SAW matched filter can be constructed and miniaturized, and S of the synchronization signal of a communication system using the SAW matched filter can be constructed.
The N ratio is improved, and highly reliable communication becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a SAW matched filter according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a SAW matched filter according to a second embodiment of the present invention.

FIG. 3 is a conceptual diagram when a split electrode is used in the SAW matched filter of the present invention.

FIG. 4 is an output IDT of the SAW matched filter of the present invention.
3 is a conceptual diagram in the case of using a three-phase unidirectional IDT in FIG.

FIG. 5 is an input IDT of the SAW matched filter of the present invention.
It is a conceptual diagram when a horn is used between the output IDT and.

FIG. 6 is an input IDT of the SAW matched filter of the present invention.
FIG. 3 is a conceptual diagram in the case of using an abodized electrode in FIG.

FIG. 7 is a block diagram showing an example of a communication system using the surface acoustic wave device of the present invention.

FIG. 8 is a block diagram showing an example of a transmitter of a communication system using the surface acoustic wave device of the present invention.

FIG. 9 is a block diagram showing an example of a receiver of a communication system using the surface acoustic wave device of the present invention.

FIG. 10 is a schematic diagram of a conventional SAW matched filter.

[Explanation of symbols]

101 Stem for fixing a matched filter chip 102 Piezoelectric substrate such as ST-cut quartz crystal 111 Input ID for converting an electric signal to a surface acoustic wave signal
T 121 Pins 122 and 123 for supplying an IF signal in which the spread spectrum signal is matched with the input center frequency of the matched filter Pins 131 and 132 for extracting an output signal Output IDT 1311, 1312, 1313, ... 131x electrode finger pair of output IDT 131 1321, 1322, 1323, ..., 132x electrode finger pair of output IDT 132 200 60 ° phase shifter 40 transmitter 401 transmitter antenna 41 receiver 411 receiver antenna 412 high-frequency signal processor 413 Synchronization circuit 414 Code generator 415 Spreading demodulation circuit 416 Demodulation circuit 501 Serial / parallel converter 502-1 to n multiplier group 503 for converting data input in series to n parallel data Spreading code generator 504 Adder 505 High frequency stage 506 Transmission antenna 60 Receiving antenna 602 high-frequency signal processing section 603 synchronizing circuit 604 spread code generator 605 carrier reproducing circuit 606 baseband demodulation circuit 607 serializer

Front page continued (72) Inventor Koichi Egara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akihiro Koyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akira Torizawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (9)

[Claims] 1. A predetermined code string is generated by exciting an input code string signal as a surface acoustic wave (hereinafter, SAW) signal by an input comb-shaped electrode (hereinafter, referred to as input IDT) formed on a piezoelectric substrate. The electrode finger pair of the output comb-shaped electrode (hereinafter, referred to as output IDT) arranged according to
A surface acoustic wave device used for a SAW matched filter that detects a signal of a code string that matches the code string by receiving an AW signal, the surface acoustic wave device having at least two output IDTs, and the two output IDTs. The input IDT is, at some point, the input I
SAW signal generated from DT is SA of the first output IDT
W is first input to the pair of electrode fingers on the input side (hereinafter referred to as the input side), and after one chip length of the code string, the input side end of the second output IDT is input. It is input to the electrode finger pair, and then sequentially alternately from the electrode finger pair closer to the input side of the first output IDT and the second output IDT at intervals of one chip length of the code string. A surface acoustic wave device characterized by being arranged. 2. The arrangement of the input IDT and the two output IDTs is such that the SAW signal generated from the input IDT through the electrode finger pair of each of the two output IDTs propagates in a time of one chip length of the code string. The first and second output IDTs are arranged at an interval corresponding to twice the distance, and the distance between the input IDT and the electrode finger pair at the input side end of the second output IDT is arranged.
Of the SAW signal generated from the input IDT rather than the distance between the electrode finger pair on the input side and the input IDT, and the distance is such that the SAW signal propagates in the time of one chip length of the code string. The surface acoustic wave device according to claim 1. 3. A predetermined code string is generated by exciting an input code string signal as a surface acoustic wave (hereinafter, SAW) signal by an input comb-shaped electrode (hereinafter, referred to as input IDT) formed on a piezoelectric substrate. The electrode finger pair of the output comb-shaped electrode (hereinafter, referred to as output IDT) arranged according to
A surface acoustic wave device for use in a SAW matched filter that detects a signal of a code string that matches the code string by receiving an AW signal, the surface acoustic wave device having at least two output IDTs, and the two output IDTs. And the input IDT, the SAW signal generated from the input IDT at a certain time is first input to the electrode finger pair at the end (hereinafter referred to as the input side) to which the SAW of the second output IDT is input. , The second output IDT is sequentially input from the pair of electrode fingers closer to the input side of the second output IDT at intervals of one chip length of the code string.
Of the electrode finger pair to be input last, after the time of the one chip length of the code string after being input to the electrode finger pair to be input last, the first output IDT is input to the electrode finger pair at the input side end, and then A surface acoustic wave device, wherein the first output IDT is arranged so as to be sequentially input from a pair of electrode fingers closer to the input side of the input IDT at intervals of one chip length of the code string. 4. The input IDT and the two output IDs
In the arrangement of T, the electrode finger pairs of the two output IDTs are arranged at intervals corresponding to the distance that the SAW signal generated from the input IDT propagates in the time of one chip length of the code string, and the first The distance between the input electrode ID and the electrode finger pair at the input side of the output IDT, and the input IDT is greater than the distance between the electrode finger pair at the end opposite to the input side of the second output IDT and the input IDT. 4. The surface acoustic wave device according to claim 3, wherein the SAW signals generated from the SAW signal are arranged at a distance apart so that they propagate in the time of one chip length of the code string. 5. The surface acoustic wave device according to claim 1, wherein the impedance of one or both of the input IDT and the output IDT is matched to a desired impedance. A surface acoustic wave device characterized in that 6. The surface acoustic wave device according to claim 1, wherein the piezoelectric substrate used for the SAW matched filter has a change in propagation velocity of the SAW with temperature of about 0, or A surface acoustic wave device characterized in that a change in propagation velocity of the SAW due to temperature is substantially zero by applying a thin film on the piezoelectric substrate. 7. The surface acoustic wave device according to claim 6, wherein the piezoelectric substrate is an ST-cut quartz substrate. 8. A receiving device, wherein the SAW matched filter of the surface acoustic wave device according to claim 1 is used as a synchronization detecting means. 9. A communication system using the surface acoustic wave device according to claim 1, wherein the SAW matched filter is synchronized with a transmission signal by a predetermined spread code sequence from a reception signal. A communication system characterized by synchronizing as a detection device.